The Microscope. 



179 



wise the glass may scratched. In all these operations the breath 

 is a useful and a harmless assistant. 



There are often found on a slide three objects that perplex the 

 beginner. These are air bubbles, oil drops and that quivering 

 and apparent dancing of minute particles called the Brownian 

 movement, or pedesis, or sometimes the pedetic motion. Air 

 bubbles have been described as wonderful things. I remember to 

 have once shown a slide of urinary deposit to a physician, who im- 

 mediately cried out that the patient must be in a dreadful condi- 

 tion, for those big, round black-bordered things surely must be 

 deadly. Like the majority of persons unaccustomed to microscopi- 

 cal investigation, he Jiad gazed at the most prominent object in 

 the field, and not at what I wanted him to see, for he had looked 

 at two or three air bubbles, that are of a truth rather frightful to 

 the uninitiated. In such cases an indicator in the eye-piece is a 

 'Useful contrivance. 



A COLONY COUNTER. 



J. EDW. LINE, F. R. M. S, 



IN the study of the comparative biology of water supplies, 

 sewage, infusions, secretions, etc., it is necessary to fix the 

 organisms in a nutrient medium, cultivate them to a given limit, 

 and make a count. To do this neatly and effectively two pieces 

 ■of apparatus are requisite, an Esmarch tube and a colony coun- 



